The extensive mid-infrared observations of comet Hale-Bopp can be
interpreted in terms of the size and composition of the dust grains.
The strong silicate emission seen in all 8 - 13 m spectra indicates
an unusually high abundance of small ( < 1 m) grains, even when the
comet was at R > 4 AU. Yet the relative strength of the 11.2 m
peak is about the same as that in other comets, implying that about 20
percent of the silicate is in the form of crystalline olivine. The
abundant small silicate grains will cause a higher mean albedo of the
dust, i.e., a stronger optical continuum per unit mass of dust, than in
other comets. The high color temperature relative to a blackbody
indicates that small hot absorbing grains are also abundant, with a mean
grain size smaller than that in most other comets. The observed color
temperature is not equal to the physical temperature of the grains,
however, because the emissivity of these small grains is wavelength-
dependent and, indeed, the observed color temperature is higher at
shorter wavelengths. Models for the size distribution and the relative
mix of silicate and absorbing grains will be presented and compared with
other comets.